What Are the Threats and Solutions?
Humans, as well as other organisms, have always utilized the waste-processing qualities of aquatic ecosystems. Controlling pollution through dilution within large water bodies has been a common solution to the accumulation of human, agricultural and industrial waste (19,1,10,11). Many systems have been effective in dealing with these excess inputs, but increased pollution through population and industrial growth has taken its toll on many aquatic systems. Some of the largest bodies of water, such as the Nile and the Mississippi Rivers, have been overloaded with waste. Human-caused threats to the provision of water purification services include the draining of wetlands, deforestation, uncontrolled pollution, and introduced species, dam construction and water diversions, and growth in human population and consumption (19,1,10,11).
The Environmental Protection Agency (EPA) estimates that approximately one third of all of the waters assessed by individual state agencies are unsafe for swimming fishing and drinking. Currently (i.e., as of 1997), 47 states have issued freshwater fish consumption advisories after evaluating the extent of pollution in their lakes and rivers. Advisories identify 45 contaminants in lakes and rivers including mercury, PCB's, chlordane, dioxin, and DDT. In 1997, there were nearly 2,200 fish consumption advisories in effect in the United States.

Pollution
In the United States, problems with water pollution came to the forefront in the 1960s and 1970s and since then a multitude of legislation and programs have been developed to protect our waterways by restricting inputs of pollution from municipal, industrial, and agricultural sources. These include the Clean Water Act, Coastal Zone Management Act, Water Resources Development Act, and Conservation Reserve Programs, among others. The Clean Water Act in particular has a major role in reducing water pollution from point sources (industrial and municipal) and non-point sources, but many of our country's rivers and streams continue to fail state and federal water quality standards (13). Much of the continued pollution can be attributed to non-point source pollution from agriculture and runoff from roads and other impervious surfaces, as well as the decrease in natural stream protection through loss of wetlands and streamside vegetation.
Water Diversion
Water diversion projects from rivers can have serious impacts on wetlands and riparian habitats both upstream and downstream and also up to several kilometers from the stream channel because of surface-groundwater connections (21). Streamflow and groundwater levels are often diminished by diverting water for use in agriculture, industry, and urban areas, and result in loss or degradation of aquatic habitats (1,11,22). Water quality and quantity problems are usually closely linked. Water extraction from rivers can result in insufficient water flow to dilute sewage inputs from sewage treatment plants. Effluent from sewage treatment plants is sometimes the sole perennial source of streamflow in arid areas of the western United States (16).

Wetland and Riparian Zone Loss
In the U.S. (excluding Alaska), more than half of the wetland area has been lost over the last two centuries (19). Stream riparian zones have also suffered declines throughout the U.S. As just one example, the state of Mississippi has lost 80% of its riparian hardwood forests. Current U.S. regulations allows for mitigation of the loss of wetlands by replacement or enhancement of the resource elsewhere. However, the complexity and temporal variation within ecosystems make it hard to develop reliable models for restoration and construction of wetlands and many of the services that wetlands supply can not be replaced. Recent research into the results of these exchanges has triggered serious concerns about our ability to successfully replace lost wetlands through this "mitigation" strategy (26).
Riparian Areas
Programs to restore riparian areas along waterways have been more successful. The Chesapeake Bay Riparian Forest Buffer Initiative, for example, seeks to protect streams and shorelines within the watershed through restoration and protection of forests and riparian buffers. Its goals include the restoration of 2,010 miles of stream and shoreline by 2010 (12).

Resources
Resources should be focused on wetlands and riparian area protection, restoration, and construction in order to diminish loss and even increase acreage. The drinkable water supply for a large percentage of the population in the United States comes from watersheds that are protected to some degree. Over half of the human population in the western United States derive water supplies from National Forest watersheds which are managed by the U.S. Forest Service (23). Increased understanding of wetland ecology, enhanced efforts in improving restoration technologies for wetlands and riparian areas, and increased financial and political resources will be necessary.
Planning
Finally, proper planning should be part of all urban, industrial, and agricultural development. The impact on waterways must be considered in planning of sewage and industrial treatment facilities and placement of feedlots. City stormwater systems should be developed to minimize the movement of oil, salt, and other pollutants from city streets into waterways. An emphasis on long term planning and the inclusion of ecological knowledge in land and water use decisions are essential to move us away from the current trend of loss of wetlands and riparian zones.